Technical Field
Embodiments of this disclosure generally relate to a laminate-type power storage element that houses a power generation element in an exterior body formed of laminated films and a card electronic device that incorporates the power storage element.
Related Art
Recently, an extremely thin electronic device (hereinafter, a thin electronic device) that incorporates a power supply, such as an IC card with a one-time password function and a display, an IC card with display, a tag, and a token (one-time password generator), has been put into practical use. To achieve these thin electronic devices, downsizing and thinning a power storage element (such as a primary battery, a secondary battery, and an electric double layer capacitor), which serves as a power supply, is necessary. As the power storage element appropriate for the downsizing and the thinning, there has been provided a laminate-type power storage element.
FIGS. 1A and 1B illustrate a laminated lithium primary battery as a conventional example for the laminate-type power storage element. FIG. 1A is an external view of a laminate-type power storage element 1a, and FIG. 1B is an exploded perspective view illustrating an internal structure of this power storage element 1a. As illustrated in FIG. 1A, the laminate-type power storage element 1a has a flat plate-shaped appearance. An exterior body 11 formed of laminated films shaped into a flat rectangular bag internally seals a power generating element. In the laminate-type power storage element 1a illustrated here, a positive electrode terminal plate 24 and a negative electrode terminal plate 34 are guided outside from one side of the rectangular exterior body 11.
Next, the following describes a structure of the laminate-type power storage element 1a with reference to FIG. 1B. FIG. 1B hatches proper positions as necessary for easy distinction of members and portions. The exterior body 11 internally seals an electrode body 10 together with an electrolytic solution. The electrode body 10 is formed by press-bonding a sheet-shaped positive electrode 20 and a sheet-shaped negative electrode 30 laminated via a separator 40. The positive electrode 20 is formed by applying a slurry positive electrode material 22 containing a positive-electrode active material such as a manganese dioxide over one principal surface of a positive electrode current collector 21 made of a metal foil or a similar material and drying the one principal surface. The positive electrode material 22 is applied over a surface of the positive electrode current collector 21 on a side opposed to the separator 40. In this example, a rectangular convex portion 23 is formed integrally with the positive electrode current collector 21. A distal end of this convex portion 23 is exposed outside of the exterior body 11 and forms the positive electrode terminal plate 24. Needless to say, a separate strip-shaped metal plate and a metal foil may be mounted to the positive electrode current collector 21, and the metal plate and the metal foil may be configured as the positive electrode terminal plate 24.
Meanwhile, the negative electrode 30 employs a flat plate-shaped metal lithium or lithium metal (hereinafter, a negative electrode lithium 32) as a negative-electrode active material. This negative electrode lithium 32 is press-bonded to a negative electrode current collector 31 formed of a metal foil, which is formed integrally with a rectangular convex portion 33. A distal end of the convex portion 33 of the negative electrode current collector 31 is configured as the negative electrode terminal plate 34. Needless to say, the negative electrode terminal plate 34 can also be configured separate from the negative electrode current collector 31.
The exterior body 11 is formed by welding peripheral edge regions 12 of two rectangular laminated films (11a and 11b) stacked on one another by the thermocompression bonding method to seal an inside of the laminated films 11a and 11b. As is well-known, the laminated films (11a and 11b) have a structure where resin layers are laminated on front and back of a metal foil (aluminum foil, stainless steel foil) serving as a base material. Generally, the laminated films (11a and 11b) have a structure where a first resin layer (hereinafter, a protection layer) made of, for example, a polyamide resin laminated on one surface and a second resin layer with thermal weldability (hereinafter, an adhesive layer) made of, for example, a polypropylene laminated on the other surface. The protection layer and the adhesive layer are possibly constituted of the single resin layer made of one resin material. Alternatively, the protection layer and the adhesive layer are each possibly additionally constituted of a plurality of resin layers. The protection layers in the laminated films (11a and 11b) face outside of the laminate-type power storage element 1a with respect to the metal foil and, for example, have a function of protecting the laminate-type power storage element 1a from an external environment (such as ultraviolet rays, temperature, and humidity). The adhesive layers, which are disposed on inner sides of the exterior body 11, bond the mutual two laminated films (11a and 11b) together by laminating the two laminated films (11a and 11b) and melting the laminated films (11a and 11b) during the thermocompression bonding.
With the laminate-type power storage element shipped as a product, after an electrode body is sealed inside an exterior body and the assembly is completed, information on the product (hereinafter, a label), such as polarity signs of + and −, a product name, a lot number, a serial number, and a date of manufacturing is printed on the surface of the exterior body. Alternatively, a paper or a similar medium on which the label has been printed is pasted. FIG. 1A illustrates the example where the label is printed directly on the surface of the exterior body 11 using an industrial inkjet printer. For example, the following Japanese Unexamined Patent Application Publication No. 2006-281613 also discloses the structure of the laminate-type power storage element and a similar specification. Non-Patent Literature (FDK CORPORATION, “Thin Type Primary Lithium Batteries,” [online], [searched on Dec. 9, 2015], Internet <URL: http://www.fdk.co.jp/battery/lithium/lithium_thin.html> (<URL: http://www.fdk.com/battery/lithium_e/lithiun_thin.html> in English)) describes features, discharge performance, and a similar specification of the thin lithium batteries, actually commercially available laminate-type power storage elements.
As described above, as the label disposed on the exterior body of the laminate-type power storage element, a printed matter (hereinafter also referred to as a print label), a matter printed on a paper or a similar medium and pasted (hereinafter also referred to as a label seal), and a similar label are available. The lot number, the serial number, or the date of manufacturing included in the label is also the information to individually manage qualities of the laminate-type power storage elements as the products. These information included in the label are used to identify a cause of a failure and to recover the individual body with failure in case of some sort of failure in the product.
However, it has been found that the conventional laminate-type power storage element has a problem in deterioration of a display quality of the label, resulting in failing to recognize the information shown in the label. As the cause of the deterioration in the label, the following is given first. For example, in the case where the laminate-type power storage element is incorporated into an electronic device, the label is in contact with a circuit component, a casing of the electronic device, or a similar component. This causes the ink to be faint and patchy and the pasted label seal to peel off.
With the well-known IC card (such as a credit card), regardless of presence/absence of a built-in power supply, the thickness is specified to 0.76 mm in accordance with standard. With the use of the laminate-type power storage element as the power supply for the card electronic device such as the IC card, the label seal pasted on the surface of the exterior body thickens the exterior body at the pasted part; therefore, the label seal is unsuitable for an application to the incorporation into the card electronic device. Accordingly, the print label is used for the laminate-type power storage element incorporated into the card electronic device and further the laminate-type power storage element itself is designed to be extremely thin. For example, the laminate-type power storage element (thin lithium battery) disclosed in the Non-Patent Literature has an extremely thin thickness of around 0.4 mm.
However, the following has been proved recently. The use of the laminate-type power storage element with the print label as the power supply for the card electronic device causes a problem different from the faint and patchy of ink, the peeling of the label seal, or a similar problem caused by the structure of the card electronic device. Specifically, the card electronic device has a structure in which two film-shaped plastic plates are pasted together with adhesive. The two plastic plates sandwich the electronic circuit and the laminate-type power storage element. That is, with the card electronic device, when the two plastic plates are mutually pasted together with the adhesive in the manufacturing process, also bonding the electronic circuit and the laminate-type power storage element on the back surfaces of the plastic plates integrates the members as a single card electronic device. Therefore, in case of some sort of failure in the card electronic device, peeling off the pasted two plastic plates to identify the cause of the failure possibly peels off the print label together with the adhesive. Additionally, a solvent contained in the adhesive melts the ink forming the label, possibly blotting a character and a sign on the label. There is also a possibility that the melted ink attaches to the electronic circuit, causing an operational failure of the electronic device. If the melted ink is blotted from the back surface of the plastic plate and reaches the front surface, the appearance of the card electronic device is significantly damaged.
It is therefore an object of the present invention is to provide a laminate-type power storage element where a display quality of a label is not deteriorated due to friction and by a medical product such as a solvent and to especially provide a laminate-type power storage element suitable for a power supply for a card electronic device and a card electronic device incorporating the power storage element.